Electrode for stimulating bone growth, tissue healing and/or pain control, and method of use

ABSTRACT

A system for use in stimulating at least one of bone growth, tissue healing and pain control in a patient includes a first screw and a second screw. The first screw has an elongate shaft with opposite ends and a length extending between the ends, an exterior surface and a screw thread formed on the exterior surface of the shaft and extending along at least a portion of the length. The screw thread has an electrically conducting portion and an electrically insulating portion. The electrically conducting portion is located for deposition in a first pre-specified portion of the patient and the electrically insulating portion is located for deposition in a second pre-specified portion of the patient. An electrical power source is adapted to pass electrical current through the patient between the first and second screws. The electrical power source is operatively connected to the first screw for conveying current through the electrically conducting portion of the screw thread to the first pre-specified portion. The electrically insulating portion inhibits current from being conveyed to the second pre-specified portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application claiming priority fromU.S. patent application Ser. No. 12/089,104 filed on Aug. 30, 2008,which claims priority from U.S. Provisional Patent Application Ser. No.60/813,633 filed on Oct. 3, 2005 and PCT Patent Application No.PCT/US2006/038699 filed on Oct. 3, 2006. Each of these applications isincorporated herein by reference in their entirety.

FIELD

The present invention relates generally to stimulating bone growth andtissue healing, and more particularly to a method and apparatus forstimulating bone growth and tissue healing by applying an electricalcurrent to the bone and adjacent soft tissue through a partiallyinsulated screw.

BACKGROUND

Bone growth is desirable in many instances, such as when vertebrae in apatient's spine are fused to overcome pain and other effects caused byinter-vertebral movement or intra-vertebral movement. Although bonegrowth occurs naturally, it can be stunted or stopped by various factorssuch as tobacco, alcohol and steroid usage, poor bone stock, and age.Moreover, stimulating bone growth to speed recovery is desirable in someinstances such as when an injured athlete wishes to return to her sportquickly. Thus, there is a need for stimulating bone growth inindividuals.

Bone growth can be stimulated by various means. One such means forstimulating bone growth is by passing an electrical current through thebone. When fusing vertebrae in a patient's spine, various means havebeen used to stimulate bone growth. For example, some stimulatorsinclude wire electrodes embedded in bone fragments grafted to a regionof the patient's back containing the vertebrae to be fused. Directelectrical current is applied to the electrodes to stimulate bone growthand fuse the fragments and adjoining vertebrae. To permit the current tobe applied for extended periods of time while permitting the patient tobe mobile, a generator is connected to the wire electrodes and implantedbetween the skin and muscle near the patient's vertebral column. Thegenerator provides a continuous low amperage direct current (e.g., 20μA) for an extended period of time (e.g., six months). After thevertebrae are fused, the generator and leads are surgically removed.Although these embedded electrodes are generally effective, the wireelectrodes are susceptible to failure, requiring additional surgery torepair them. Moreover, placement of the wire electrodes is less thanprecise, allowing some of the current to pass through areas of tissueand bone where it is unneeded and where the current could potentiallyhave adverse effects. Further, imprecise placement may require moreenergy to be provided to the electrodes than otherwise necessary to beoptimally effective. Thus, there are several drawbacks and potentialproblems associated with devices such as these.

Although small amounts of bone movement can stimulate growth, it isgenerally desirable to limit movement between the bones or bonefragments being fused. There are several known means for limiting bonemovement. Among these means for limiting bone movement are plates, rodsand screws.

The plates and rods are typically held in position by screws which aremounted in the bone or bones being fused. FIG. 1 illustrates screws(generally designated by 10) driven into a vertebra 12 to immobilize thevertebra. As previously mentioned, the screws 10 are used for attachingrods 14 and/or plates (not shown) to vertebrae to hold the vertebrae inposition while they fuse. Although these screws work well for theirintended purpose, they do not facilitate electrically stimulating theregion. Moreover, if electrical stimulation were applied to bones havingconventional screws, the screws could potentially conduct current toareas of tissue and bone where the current is unneeded and where thecurrent could potentially have adverse effects. Thus, there aredrawbacks and potential problems associated with conventional screwssuch as these.

Beyond the well defined role of electrical fields within bone formation,electrical fields have also shown significant promise in aiding healingand recovery in nerve and spinal cord injury. Stimulating tissue healingwith electrical currents has been demonstrated to be efficacious inanimal models and is now being attempted experimentally in humansubjects. Further, spinal cord and nerve root injury has been known tocause associated debilitating pain syndromes which are resist treatment.These pain syndromes also have shown improvement with pulsed electricalstimulation. Given these findings it is envisioned that apparatusproviding a specified and confined electrical field through bonyconstructs and adjacent tissue (e.g., neural tissue) will facilitate anenhanced recovery from spinal cord and nerve injury, including improvedfunctional outcome, better wound healing, and a higher level of paincontrol.

SUMMARY

In one aspect, a system for use in stimulating at least one of bonegrowth, tissue healing and pain control in a patient generally comprisesa first screw and a second screw. The first screw has an elongate shaftwith opposite ends and a length extending between the ends, an exteriorsurface and a screw thread formed on the exterior surface of the shaftand extending along at least a portion of the length. The screw threadhas an electrically conducting portion and an electrically insulatingportion. The electrically conducting portion is located for depositionin a first pre-specified portion of the patient and the electricallyinsulating portion is located for deposition in a second pre-specifiedportion of the patient. An electrical power source is adapted to passelectrical current through the patient between the first and secondscrews. The electrical power source is operatively connected to thefirst screw for conveying current through the electrically conductingportion of the screw thread to the first pre-specified portion. Theelectrically insulating portion inhibits current from being conveyed tothe second pre-specified portion.

In another aspect, a system for use in stimulating at least one of bonegrowth, tissue healing and pain control in a patient generally comprisesa first screw having an elongate shaft with opposite ends and a lengthextending between the ends, an exterior surface and a screw threadformed on the exterior surface of the shaft and extending along at leasta portion of the length. The screw thread has an electrically conductingportion and an electrically insulating portion. The electricallyconducting portion is located for deposition in a first pre-specifiedportion of the bone and bone related tissue and the electricallyinsulating portion is located for deposition in a second pre-specifiedportion of the bone and bone related tissue. A second screw has anelongate shaft with opposite ends and a length extending between theends, an exterior surface and a screw thread formed on the exteriorsurface of the shaft and extending along at least a portion of thelength. The screw thread has an electrically conducting portion and anelectrically insulating portion. The electrically conducting portion islocated for deposition in the first pre-specified portion of the boneand bone related tissue and the electrically insulating portion islocated for deposition in the second pre-specified portion of the boneand bone related tissue. An electrical power source is adapted to passelectrical current between the first and second screw.

In yet another aspect, a system for use in stimulating at least one ofbone growth, tissue healing and pain control in a patient generallycomprises a first screw and a second screw. The first screw has anelongate shaft with opposite ends and a length extending between theends, an exterior surface and a screw thread formed on the exteriorsurface of the shaft and extending along at least a portion of thelength. The screw thread has an electrically conducting portion and anelectrically insulating portion. The electrically conducting portion islocated for deposition in a first pre-specified portion of the patientand the electrically insulating portion is located for deposition in asecond pre-specified portion of the patient. A plate has at least twoopenings sized and shaped for receiving the first and second screws. Anelectrical power source is adapted to pass electrical current betweenthe first and second screw. The electrical power source is operativelyconnected to the first screw for conveying current through theelectrically conducting portion of the screw thread to the firstpre-specified portion. The electrically insulating portion inhibitscurrent from being conveyed to the second pre-specified portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a horizontal cross section of a conventional electricallyconductive screw installed in a vertebra;

FIG. 2 is a side elevation of a screw of the present invention;

FIG. 3 is a cross section of the screw taken along line 3-3 of FIG. 2;

FIG. 4 is an front elevation of a portion of a spine with a firstapparatus of the present invention installed thereon; and

FIG. 5 is a side elevation of a portion of a spine with a secondapparatus of the present invention installed thereon.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION AN EMBODIMENT

Referring now to the drawings and in particular to FIG. 2, a screw orelectrode of the present invention is designated in its entirety by thereference numeral 20. The screw 20 has an elongate shaft 22 having alength 24 (FIG. 3) extending between opposite ends 26, 28. Aconventional screw thread 30 is formed on an exterior surface 32 of theshaft 22. The thread 30 extends along at least a portion of the length24 of the shaft 22. The screw 20 also includes a head 34 adjacent theone end 28 of the shaft 22. The head 34 is shaped for engaging the screw20 with a driver or wrench to rotate the screw and thereby drive it intobone. In one embodiment, the head 34 includes a connector, generallydesignated by 36, adjacent its head 34 for connecting an electricalconductor to the screw 20 as will be explained in further detail below.In one embodiment, the connector 36 includes a screw fastener 38threaded into the screw 20 for holding the electrical lead. Asillustrated in FIG. 2, an electrical conductor 40 is electricallyconnectable to the screw 20 and to an electrical power source 42 forconveying electrical current through the shaft. In one embodiment thepower source 42 produces direct current. In another embodiment, thepower sources 42 produces alternating current such as a time-varyingcurrent waveform (e.g., a sine wave or a square wave) having a frequencybetween nearly zero hertz and ten gigahertz. Although other electricalconductors 40 may be used without departing from the scope of thepresent invention, in one embodiment the conductor is a 35 gaugeinsulated braided stainless steel wire. It is further envisioned thatthe connector 36 may take other forms. For example, the connector may bea threaded terminal and nut, a fastenerless connector, a quickdisconnect type connector, a soldered pin, or an adhesive withoutdeparting from the scope of the present invention.

As illustrated in FIG. 3, the shaft 22 is generally conductive, but aportion of the shaft is coated with an insulating coating 50. Thus, theshaft 22 has an electrically conducting portion 52 and an electricallyinsulating portion 54. Although the conducting portion 52 of the screw20 may have other lengths without departing from the scope of thepresent invention, in one embodiment the conducting portion of the screwhas a length of less than about three centimeters. In one embodiment,the conducting portion 52 of the screw 20 has a length of between aboutthree millimeters and about three centimeters. Further, although theconducting portion 52 of the screw 20 may be positioned at otherlocations along the screw, in one embodiment the conducting portion ofthe screw is positioned adjacent the end 26 of the screw opposite thehead 34. In another embodiment (not shown), the conducting portion 52 ofthe screw 20 is positioned between the ends 26, 28 of the screw, andeach end of the screw is electrically insulated. Although the insulatingportion 54 of the screw 20 may have other lengths without departing fromthe scope of the present invention, in one embodiment the insulatingportion of the shaft extends at least forty percent of the length of thescrew. In another embodiment, the insulating portion 54 of the shaft 22extends between about fifty percent of the length of the screw 20 andabout ninety five percent of the length of the screw.

In one embodiment, a clevis 60 is attached to the screw 20. The clevis60 pivots freely on the head 34 of the screw and includes a pair of legs62 defining an opening 64 adapted to receive a rod 66. The legs 62include threads 68 for engaging a screw 70 for fastening the rod 66 inthe opening 64 and preventing the clevis 60 from pivoting on the screwhead 34. Other features of the screw 20 and clevis 60 are conventionaland will not be described in further detail.

As will be appreciated by those skilled in the art, the screw 20comprises an electrically conductive material such as a titanium alloyand the electrically insulating portion of the shaft is coated with aninsulating material such as titanium dioxide. In one embodiment, theinsulating material is formed by anodizing the exterior surface of aportion of the shaft. The conductivity of the screw 20 in the conductingportion 52 may be improved by coating the screw with a highly conductivematerial such as titanium nitride. Both treated surfaces, titaniumdioxide and titanium nitride, are extremely adherent to the titanium andtherefore not likely to be breached when screwed into bone. Becausemethods for anodizing and/or coating titanium parts are well known bythose having ordinary skill in the art, they will not be described infurther detail.

The screws 20 are used in pairs so an electrical circuit is completedfrom the bone into which the screws are driven. As will be appreciatedby those skilled in the art, the current travels through the conductiveportion of the screw 20 from the conductor 40 to the bone in which thescrew 20 is inserted (e.g., a vertebra such as vertebra 12 in FIG. 1) aswill be explained in more detail below. The current does not passthrough the coating on the insulated portion 54 of the shaft 22 so thatthe current may be directed to the portion of the bone where stimulationis most needed. As will be also appreciated, the insulated portion 54 ofthe shaft 22 prevents current from passing through portions of the boneand tissue where electrical current is not desired. The screw 20 of thepresent invention may be installed in the bone using conventionaltechniques. In most instances, the bone is pre-drilled to avoidsplitting when the screw 20 is installed. It is envisioned in someinstances the bone may be reinforced, such as with bands before thescrew 20 is installed to provide support to the bone and prevent damageto it as the screw is installed.

In some instances, it is envisioned that the screws 20 of the presentinvention may be used in combination with other appliances such asspacers. For example, in some applications the screws 20 may beinstalled through a plate 80 as shown in FIG. 4 to provide support forthe bone and to guide proper spacing and positioning of the screws. Theplate 80 has at least two openings (not shown) for receiving screws 20.Preferably, each of the openings are sized and shaped for receiving atleast one screw 20. Although the openings in the plate 60 may have otherspacings without departing from the scope of the present invention, inone embodiment the openings are spaced by a distance 82 of between aboutone centimeter and about two centimeters. In the embodiment shown inFIG. 5, the spacers are formed as rods 66 bridging the screws 20 asdescribed above. As the configurations shown in FIGS. 4 and 5 are wellknown to those having ordinary skill in the art, they will not bedescribed in further detail.

To use the apparatus of the present invention to stimulate bone growth,the bone (e.g., vertebra 12) is pre-drilled. A first screw 20 isinserting in the bone and driven into place by turning the screw. Asecond screw 20 is inserted in the bone at a predetermined distance fromthe first screw. Next, electrical conductors 40 are attached to thescrews 20 and to an electrical power source 42 (e.g., a generator, abattery or an inductance coil positioned in a pulsing magnetic field).The conductors 40 are energized by the power source 42 so an electricalcurrent passes through the bone. Because the screws 20 are partiallyinsulated, the electrical current passes between only a portion of thefirst screw and only a portion of the second screw directing the currentto a particular area of the bone or tissue. Although other amounts ofcurrent may be used, in one embodiment a direct current of between aboutone microamp and about one milliamp is used. In another embodiment, adirect current of between about twenty microamps and about sixtymicroamps is used. In other embodiments, the current may be anytime-varying current waveform (e.g., a sine wave or a square wave)having a frequency between nearly zero hertz and ten gigahertz.

In addition to stimulating bone growth, it is envisioned that theapparatus and method described above may be used to improve tissuegrowth and healing, including soft tissue and nerve tissue. Thus, theapparatus and method may be useful in healing spinal cord and nerve rootinjury. Further, the apparatus and method may be useful in treating painsyndromes.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. A system for use in stimulating at least one ofbone growth, tissue healing and pain control in a patient, the systemcomprising: a first screw having an elongate shaft with opposite endsand a length extending between the ends, an exterior surface and a screwthread formed on the exterior surface of the shaft and extending alongat least a portion of the length, said screw thread having anelectrically conducting portion and an electrically insulating portion,the electrically conducting portion being located for deposition in afirst pre-specified portion of the patient and the electricallyinsulating portion being located for deposition in a secondpre-specified portion of the patient; a second screw; and an electricalpower source adapted to pass electrical current through the patientbetween the first and second screws, the electrical power source beingoperatively connected to the first screw for conveying current throughthe electrically conducting portion of the screw thread to the firstpre-specified portion, the electrically insulating portion inhibitingcurrent from being conveyed to the second pre-specified portion.
 2. Thesystem set forth in claim 1 wherein the electrical power source isadapted to pass direct current between the first and second screws. 3.The system set forth in claim 2 wherein the electrical power source isadapted to pass direct current between about one microamp and about onemilliamp between the first and second screws.
 4. The system set forth inclaim 3 wherein the electrical power source is adapted to pass directcurrent between about twenty microamps and about sixty microamps betweenthe first and second screws.
 5. The system set forth in claim 1 whereinthe electrically conducting portion of the first screw is located fordeposition in bone of the patient.
 6. The system set forth in claim 1wherein the electrically conducting portion of the first screw islocated for deposition in at least one of soft tissue and nerve tissueof the patient.
 7. The system set forth in claim 1 further comprising aplate having at least two openings therein for receiving the first andsecond screws.
 8. The system set forth in claim 7 wherein the openingsin the plate are spaced by a distance of between about one centimeterand about ten centimeters.
 9. A system for use in stimulating at leastone of bone growth, tissue healing and pain control in a patient, thesystem comprising: a first screw having an elongate shaft with oppositeends and a length extending between the ends, an exterior surface and ascrew thread formed on the exterior surface of the shaft and extendingalong at least a portion of the length, said screw thread having anelectrically conducting portion and an electrically insulating portion,the electrically conducting portion being located for deposition in afirst pre-specified portion of the bone and bone related tissue and theelectrically insulating portion being located for deposition in a secondpre-specified portion of the bone and bone related tissue; a secondscrew having an elongate shaft with opposite ends and a length extendingbetween the ends, an exterior surface and a screw thread formed on theexterior surface of the shaft and extending along at least a portion ofthe length, said screw thread having an electrically conducting portionand an electrically insulating portion, the electrically conductingportion being located for deposition in the first pre-specified portionof the bone and bone related tissue and the electrically insulatingportion being located for deposition in the second pre-specified portionof the bone and bone related tissue; and an electrical power source forpassing electrical current between the first and second screw.
 10. Thesystem set forth in claim 9 wherein the electrical power source isadapted to pass direct current between the first and second screws. 11.The system set forth in claim 10 wherein the electrical power source isadapted to pass direct current between about one microamp and about onemilliamp between the first and second screws.
 12. The system set forthin claim 11 wherein the electrical power source is adapted to passdirect current between about twenty microamps and about sixty microampsbetween the first and second screws.
 13. The system set forth in claim 9wherein the electrical power source is adapted to pulse electricalcurrent between the first and second screws.
 14. The system set forth inclaim 9 wherein the electrical power source is adapted to pulseelectrical current between the first and second screws.
 15. The systemset forth in claim 9 wherein the electrical power source is adapted todirect a current having a frequency less than 10 gigahertz between thefirst and second screws.
 16. A system for use in stimulating at leastone of bone growth, tissue healing and pain control in a patient, thesystem comprising: a first screw having an elongate shaft with oppositeends and a length extending between the ends, an exterior surface and ascrew thread formed on the exterior surface of the shaft and extendingalong at least a portion of the length, said screw thread having anelectrically conducting portion and an electrically insulating portion,the electrically conducting portion being located for deposition in afirst pre-specified portion of the patient and the electricallyinsulating portion being located for deposition in a secondpre-specified portion of the patient, a second screw; a plate having atleast two openings sized and shaped for receiving the first and secondscrews; and an electrical power source for passing electrical currentbetween the first and second screw, the electrical power source beingoperatively connected to the first screw for conveying current throughthe electrically conducting portion of the screw thread to the firstpre-specified portion, the electrically insulating portion inhibitingcurrent from being conveyed to the second pre-specified portion.
 17. Thesystem set forth in claim 16 wherein the openings in the plate arespaced by a distance between about one centimeter and about tencentimeters.
 18. The system set forth in claim 17 wherein the openingsin the plate are spaced by a distance between about one centimeter andabout two centimeters.
 19. The system set forth in claim 16 furthercomprising a rod bridging the first and second screws.
 20. The systemset forth in claim 16 wherein the electrically conducting portion islocated for deposition in a vertebra of the patient.